I bought a house with a Navien NCB-240e combi boiler. It has been nothing but problems. Thousands of dollars in repair costs and completely useless support.
My last call to support was this morning and because of their "internal processes" they wouldn't help and then they hung up on me when I asked to speak to a supervisor.
During one of my first repairs the plumber advised me to replace it. I wish I had listened.
Based on my experience i don't ever expect to purchase a Navien product again.
Recommendation: Don't buy Navien Products